[PATCH v2] x86: fix "REP RET" with -madd-bnd-prefix

[Jan Beulich]

Just like any other branches, RET should gain a BND prefix also when
already prefixed in source by REP.

gas/
2018-07-10  Jan Beulich  <jbeulich@suse.com>

	* config/tc-i386.c (md_assemble): Also replace an already
	present REP prefix.
	* testsuite/gas/i386/mpx-add-bnd-prefix.s,
	testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.s: Test RET with
	all REP flavors.
	* testsuite/gas/i386/mpx-add-bnd-prefix.d,
	testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.d: Adjust
	expectations.
	* testsuite/gas/i386/mpx-add-bnd-prefix.e,
	testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.e: New.

---
v2: Warn when replacing REP/REPE with BND.

--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -4112,10 +4112,16 @@ md_assemble (char *line)
     }
 
   /* Insert BND prefix.  */
-  if (add_bnd_prefix
-      && i.tm.opcode_modifier.bndprefixok
-      && !i.prefix[BND_PREFIX])
-    add_prefix (BND_PREFIX_OPCODE);
+  if (add_bnd_prefix && i.tm.opcode_modifier.bndprefixok)
+    {
+      if (!i.prefix[BND_PREFIX])
+	add_prefix (BND_PREFIX_OPCODE);
+      else if (i.prefix[BND_PREFIX] != BND_PREFIX_OPCODE)
+	{
+	  as_warn (_("replacing `rep'/`repe' prefix by `bnd'"));
+	  i.prefix[BND_PREFIX] = BND_PREFIX_OPCODE;
+	}
+    }
 
   /* Check string instruction segment overrides.  */
   if (i.tm.opcode_modifier.isstring && i.mem_operands != 0)
--- a/gas/testsuite/gas/i386/mpx-add-bnd-prefix.d
+++ b/gas/testsuite/gas/i386/mpx-add-bnd-prefix.d
@@ -1,4 +1,5 @@
 #as: -madd-bnd-prefix
+#stderr: mpx-add-bnd-prefix.e
 #objdump: -drw
 #name: Check -madd-bnd-prefix
 
@@ -18,7 +19,9 @@ Disassembly of section .text:
 0+14 <foo>:
 [ 	]*[a-f0-9]+:	f2 c3                	bnd ret 
 [ 	]*[a-f0-9]+:	f2 c3                	bnd ret 
-[ 	]*[a-f0-9]+:	f2 e8 f6 ff ff ff    	bnd call 14 <foo>
+[ 	]*[a-f0-9]+:	f2 c3                	bnd ret 
+[ 	]*[a-f0-9]+:	f2 c3                	bnd ret 
+[ 	]*[a-f0-9]+:	f2 e8 f2 ff ff ff    	bnd call 14 <foo>
 [ 	]*[a-f0-9]+:	01 c3                	add    %eax,%ebx
-[ 	]*[a-f0-9]+:	e2 f2                	loop   14 <foo>
+[ 	]*[a-f0-9]+:	e2 ee                	loop   14 <foo>
 #pass
--- /dev/null
+++ b/gas/testsuite/gas/i386/mpx-add-bnd-prefix.e
@@ -0,0 +1,3 @@
+.*: Assembler messages:
+.*:12: Warning: .*rep.*bnd.*
+.*:13: Warning: .*rep.*bnd.*
--- a/gas/testsuite/gas/i386/mpx-add-bnd-prefix.s
+++ b/gas/testsuite/gas/i386/mpx-add-bnd-prefix.s
@@ -8,7 +8,9 @@
 	jmp	*(%ebx)
 	ret
 foo:
-	# Use of REPNE prefix - we shouldn't get any error
+	# Use of any REP prefix - we shouldn't get any error
+	rep ret
+	repe ret
 	repne ret
 	# BND prefix already exists - we shouldn't get any error here
 	bnd ret
--- a/gas/testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.d
+++ b/gas/testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.d
@@ -1,4 +1,5 @@
 #as: -madd-bnd-prefix
+#stderr: x86-64-mpx-add-bnd-prefix.e
 #objdump: -drw
 #name: Check -madd-bnd-prefix (x86-64)
 
@@ -18,7 +19,9 @@ Disassembly of section .text:
 0+14 <foo>:
 [ 	]*[a-f0-9]+:	f2 c3                	bnd retq 
 [ 	]*[a-f0-9]+:	f2 c3                	bnd retq 
-[ 	]*[a-f0-9]+:	f2 e8 f6 ff ff ff    	bnd callq 14 <foo>
+[ 	]*[a-f0-9]+:	f2 c3                	bnd retq 
+[ 	]*[a-f0-9]+:	f2 c3                	bnd retq 
+[ 	]*[a-f0-9]+:	f2 e8 f2 ff ff ff    	bnd callq 14 <foo>
 [ 	]*[a-f0-9]+:	48 01 c3             	add    %rax,%rbx
-[ 	]*[a-f0-9]+:	e2 f1                	loop   14 <foo>
+[ 	]*[a-f0-9]+:	e2 ed                	loop   14 <foo>
 #pass
--- /dev/null
+++ b/gas/testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.e
@@ -0,0 +1,3 @@
+.*: Assembler messages:
+.*:12: Warning: .*rep.*bnd.*
+.*:13: Warning: .*rep.*bnd.*
--- a/gas/testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.s
+++ b/gas/testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.s
@@ -8,7 +8,9 @@
 	jmp	*(%rbx)
 	ret
 foo:
-	# Use of REPNE prefix - we shouldn't get any error
+	# Use of any REP prefix - we shouldn't get any error
+	rep ret
+	repe ret
 	repne ret
 	# BND prefix already exists - we shouldn't get any error here
 	bnd ret